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Role of imaging in salivary gland lesions
Dr. T. Balasubramanian M.S. D.L.O.
Imaging modalities available to assess salivary glands include:
These imaging modalities play an important role in evaluating a patient with pain, swelling, or other symptoms related to possible salivary gland disorders. Imaging helps in differentiating lesions of salivary glands from those of parapharyngeal space, masticator space, and mandible, submandibular and submental spaces. In addition to localizing the lesion, it also aids in determining the extent of disease, involvement of skull base, mandible, and neural spread in case of malignant lesions.
Plain film radiographs: were used to determine salivary gland abnormalities before the development of more sophisticated imaging techniques. It is the least sensitive of all the imaging modalities. It is least expensive and readily available. It will readily demonstrate calculi. It also helps in differentiating bony / cartilaginous lesions that may mimic salivary gland pathology.
Sialography is contraindicated in cases of acute infections of salivary glands.
This test is performed by injecting oil / water soluble iodine containing contrast solution into the Stenson’s / Wharton’s duct. Water soluble diatrizoate meglumine and iodipimide meglumine are preferred because of their low viscosity and ease of injection. Water soluble agents also cause very little foreign body reaction. This imaging modality is very rarely used in sublingual imaging because the ducts are numerous and small. They open directly to the floor of the mouth. Sublingual Sialography is possible only in patients with anatomic variations like filling up of Bartholin’s duct from injection of Wharton’s duct during submandibular Sialography.
Since about 80% of salivary gland calculi are radio opaque, plain film study is a must before Sialography.
CT scan: This has revolutionized salivary gland imaging. It provides precise anatomical detail and is routinely used as a primary imaging modality in salivary gland lesions. It is very useful in evaluating salivary gland calculi and associated adnexal inflammation. It is inferior to Sialography in studying the ductal system.
CT of parotid gland is obtained by using thin section slices in axial and rarely coronal images. This is usually performed after intravenous injection of contrast solution. Mild enhancement of parotid gland takes place after contrast injection. Images are usually filmed with conventional soft tissue windows. Bone windows are useful for evaluating calcification, calculi formation, or adjacent bone involvement.
MRI: Usually is complementary to CT because of its excellent soft tissue delineation capability. It is better than CT in differentiating parotid from extra parotid masses.
Ultrasonography: High resolution Ultrasonography (7.5 – 10 MHz) of parotid and submandibular salivary glands is actually a quick and non invasive method for assessing these glands. It helps in the assessment of vascularity of the gland, whether the lesion is solid or cystic. It also helps in accurately guiding the FNAC needle to perform biopsy from the suspected lesion.
Color Doppler studies of salivary glands indirectly identifies malignant lesions of salivary glands as these lesions boast high vascularity in comparison with their benign counterparts.
Radionuclide imaging: Is rarely used to evaluate salivary glands. Sodium pertechnetate (technetium 99m) is the commonly used element. This isotope is concentrated and excreted by salivary glands. Since most salivary gland tumors do not accumulate the radionuclide, a tumor mass will appear as a filling defect on this scan. Tumors like warthin’s readily take up pertechnetate resulting in formation of “Hot spots”.